Solar power without solar cells: It could be possible

David Gomez, 14th April 2011

A new discovery by scientists could lead to solar power without the usual semiconductor-based solar cells.

Yes, this amazing breakthrough via a magnetic effect was developed by University of Michigan scientists.

Science can be pretty crazy sometimes, and the craziness has allowed the researchers to find a method to make an “optical battery,” said Stephen Rand, a professor in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics.

Oh, and during that process, they basically overturned a century-old tenet of physics. No big deal right?

“You could stare at the equations of motion all day and you will not see this possibility. We’ve all been taught that this doesn’t happen,” said Rand, an author of a paper on the work published in the Journal of Applied Physics. “It’s a very odd interaction. That’s why it’s been overlooked for more than 100 years.”

As you may know, light has electric and magnetic components. And up until now, scientists thought that the effects of light’s magnetic field were so puny that they could be ignored. They were wrong.

Rand and his team found out that at the right intensity, when light is traveling from end to end in a material that does not conduct electricity, the light field can produce magnetic effects that are 100 million times stronger than what scientists expected. With these conditions, the magnetic effects stimulate strength equal to a robust electric effect.

“This could lead to a new kind of solar cell without semiconductors and without absorption to produce charge separation,” Rand said. “In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light and then it is ultimately capable of providing a capacitive power source.”

The thing that makes this “magic” possible is a formerly unnoticed type of “optical rectification,” says William Fisher, a doctoral student in applied physics. In customary optical rectification, light’s electric field generates a charge separation, or a pulling apart of positive and negative charges in a material.

This leads to a voltage similar to what you’d find in a battery, if you’ve ever licked a 9 volt then you probably know a little something about voltage in batteries. This electric outcome was only detected in crystalline materials that had a certain symmetry in the past.

The scientific duo of Rand and Fisher established that under the right situations and in other types of materials, the light’s magnetic field can also create optical rectification.

“It turns out that the magnetic field starts curving the electrons into a C-shape and they move forward a little each time,” Fisher said. “That C-shape of charge motion generates both an electric dipole and a magnetic dipole. If we can set up many of these in a row in a long fiber, we can make a huge voltage and by extracting that voltage, we can use it as a power source.”

The light must be put through a substance that does not conduct electricity, like glass. Plus it must be concentrated to an intensity of 10 million watts per square centimeter. Now according to Fisher, sunlight isn’t this intense on its own, but new materials are being pursued that would work at lower intensities.

“In our most recent paper, we show that incoherent light like sunlight is theoretically almost as effective in producing charge separation as laser light is,” Fisher said.

So theoretically these guys may have finally found the breakthrough that we need to make alternative energy viable.

This new knowledge could eventually make solar power cheaper, the researchers say. They think that with upgraded materials they could attain 10 percent efficiency in converting solar power to useable energy. That’s equivalent to today’s commercial-grade solar cells. And these guys are just getting started.

“To manufacture modern solar cells, you have to do extensive semiconductor processing,” Fisher said. “All we would need are lenses to focus the light and a fiber to guide it. Glass works for both. It’s already made in bulk, and it doesn’t require as much processing. Transparent ceramics might be even better.”

In experiments this summer, the researchers will try to harness this power with laser light, and then with sunlight. We will for sure keep our eye on this new development.

For those who want to know, the paper that this information came from is titled “Optically-induced charge separation and terahertz emission in unbiased dielectrics.” It’s behind a pay wall, but we figured that some of you might have a way to read it. The university is also pursuing patent protection for the intellectual property, which might be a problem in the future. We’ll just have to wait and see.